A ternary thin film of CuInSe2 (hereinafter, referred to as “CIS”) or CuIn1-xGaxSe2 (hereinafter, referred to as “CIGS”) is a semiconductor compound that has been actively studied recently.
Unlike a conventional solar cell using silicon, such a CIS-based thin film solar cell can be fabricated to have a thickness of less than 10 μ and has stable characteristics even with prolonged use thereof. In addition, by experimentation, it has been determined to have an energy conversion efficiency of up to 19% that is superior to other solar cells and thus commercialization thereof to a lower price high efficiency solar cell capable of substituting silicon is highly promising.
In this connection, a variety of processes for producing the CIS thin film have been recently reported. For example, one method, as described in U.S. Pat. No. 4,523,051, is to vapor deposit elemental metals simultaneously under vacuum atmosphere. However, this method uses an expensive effusion cell and thus is uneconomical with respect to mass production and realization of large area. Another method, as described in U.S. Pat. No. 4,798,660, is to heat and selenize a Cu—In precursor under selenium-containing gas atmosphere such as H2Se. However, H2Se gas is highly toxic to the human body and thus dangerous in mass production of the CIS thin film. Other methods such as electrodeposition, Molecular Beam Epitaxy, and the like have been proposed, but they are expensive or feasible only on a laboratory scale, thus being unsuitable for mass production of the CIS thin film.
Therefore, in order to implement mass production of a good quality CIS thin film, it is most preferred to use Metal Organic Chemical Vapor Deposition (hereinafter, referred to as “MOCVD”) widely used in a conventional semiconductor process.
However, MOCVD is a generalized technique capable of producing a good quality thin film at lower production costs in the semiconductor industry, but production of the CIS solar cell using the conventional MOCVD technique presents problems associated with high production costs and complex process resulting in difficulty in mass production of good quality thin films.
In order to grow the CIS or CIGS thin film, a conventional process involves sputtering molybdenum to be vapor deposited on a glass substrate, and then using it as the substrate for growing the thin film. However, the glass substrate is not flexible, and thus there was a problem in which the glass substrate cannot be used in a situation requiring free deformation thereof.